Anti-seismic bearing and assembly of anti-seismic bearings

ABSTRACT

An anti-seismic bearing made up of a plurality of rigid plates and viscoelastic flexible plates laminated alternately, said flexible plates being made of a material characterized by that the hysteresis ratio at 100% deformation at 25° C. is 0.15 to 0.60, the loss tangent (tan δ) at 0.01% deformation, 5 Hz, at 25° C. is 0.010 to 0.194, and the ratio E(-10)/E(30) is 1.0 to 3.0, where E(-10) is a storage modulus at 0.01% deformation 5 Hz, at -10° C. and E(30) is a storage modulus at 0.01% deformation, 5 Hz, at 30° C. 
     An assembly composed of low-damping anti-seismic bearings and high-damping anti-seismic bearings arranged in parallel such that the anti-seismic bearings support the vertical load and undergo elastic deformation in the horizontal direction.

FIELD OF THE INVENTION AND RELATED ART STATEMENT

The present invention relates to an anti-seismic bearing of such astructure that a plurality of rigid plates and viscoelastic flexibleplates are bonded to each other alternately. More particularly, itrelates to an anti-seismic bearing having both the seismic isolatingeffect and the damping effect. It also relates to an assembly of suchanti-seismic bearings which has both the seismic isolating effect andthe damping effect so that it isolates the structure and equipment fromseismic force.

A laminate structure composed of rigid plates like steel plates andviscoelastic plates like rubber plates is commonly used as a bearingmember which is required to have the vibration insulating and absorbingproperties.

The anti-seismic bearing exhibits its function and effect when it isinserted between a rigid structure such as a concrete building and afoundation thereof. Because of its low shear modulus, it shifts thenatural frequency of a concrete building from the seismic frequency. Asthe result, the building on the anti-seismic bearings receives only avery little acceleration of earthquake. Nevertheless, the building isstill subject to the slow horizontal ground motion, which, when great,would cause damage to the building, piping, wiring, and other equipment.To reduce the displacement caused by horizontal motion, the anti-seismicbearings are installed in combination with dampers. The installation ofboth anti-seismic bearings and dampers needs complex works and adds tocost to a great extent. A conceivable way to avoid this situation is tohollow out the anti-seismic bearing and fill the hollow with lead. Leadundergoes plastic deformation at the time of earthquake, imparting thedamping effect to the anti-seismic bearing. The disadvantage of thelead-containing anti-seismic bearing is that when it greatly deforms inan energetic earthquake, the rigid plates such as steel plates damagethe lead and the damaged lead in turn damages the flexible plates suchas rubber plates, with the series of damages eventually breaking theentire anti-seismic bearing. In addition, the damaged lead readilybreaks after repeated large deformation.

There is a problem in the case where the anti-seismic bearings are usedin combination with plastic dampers made of a soft metal which undergoesplastic deformation immediately when it receives a seismic force. Theproblem is that although the dampers absorb the seismic energy,resonance occurs in the high-frequency region because the plastic damperhas a high modulus.

OBJECT AND SUMMARY OF THE INVENTION

It is an object of the present invention to provide an anti-seismicbearing which produces both the seismic isolating effect and the dampingeffect.

It is another object of the invention to provide an anti-seismic bearingwhich has the seismic isolating effect, damping effect, and creepresistance.

The anti-seismic bearing of the invention is made up of a plurality ofrigid plates and viscoelastic flexible plates laminated alternately,with the flexible plates being made of a material characterized by thatthe hysteresis ratio at 100% deformation at 25° C. is 0.15 to 0.60, theloss tangent (tan δ) at 0.01% deformation, 5 Hz, at 25° C. is 0.010 to0.194, and the ratio E(-10)/E(30) is 1.0 to 3.0, where E(-10) is astorage modulus at 0.01% deformation, 5 Hz, at -10° C. and E(30) is astorage modulus at 0.01% deformation, 5 Hz, at 30° C.

The assembly of anti-seismic bearings of the invention is composed ofhigh-damping anti-seismic bearings and low-damping anti-seismic bearingsinstalled in parallel.

In general, a damper should preferably be made of a material having ahigh hysteresis loss. Unfortunately, however, a material having a highhysteresis loss is more liable to creep and the modulus of such amaterial is more dependent on temperature. These properties are notdesirable for anti-seismic bearings to support a building. The flexibleplates constituting the anti-seismic bearing of the invention has ahysteresis loss in a specific range and also has a modulus which is lessdependent on temperatures. Therefore, they impart the seismic isolationproperty and damping property to the anti-seismic bearing.

For the assembly of anti-seismic bearings to be effective as a damper,each anti-seismic bearing should preferably have a high hysteresis loss,as mentioned above. However, a high hysteresis loss is generallyachieved when the material has a higher creep and a moretemperature-dependent modulus.

According to the present invention, anti-seismic bearings having highdamping performance and anti-seismic bearings having low dampingperformance are installed parallel in such a manner that the lattersupport a part of the vertical load. This arrangement produces the goodseismic isolating effect and damping effect.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of the anti-seismic bearingpertaining to one example of the invention.

FIG. 2 is a graph showing the stress-strain curve of a material.

FIG. 3 is a longitudinal sectional view of the anti-seismic bearingpertaining to another example of the invention.

FIG. 4 is a longitudinal sectional view of the anti-seismic bearingpertaining to further another example of the invention.

FIG. 5 is an enlarged sectional view of the part indicated by V in FIG.4.

FIG. 6 is an enlarged sectional view of the important part of theanti-seismic bearing pertaining to another example of the invention.

FIG. 7 is a sectional view of the assembly of anti-seismic bearingspertaining to an example of the invention.

FIG. 8 is a sectional view of the assembly of anti-seismic bearingspertaining to another example of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a longitudinal sectional view of the anti-seismic bearing 1pertaining to an example of the invention. The anti-seismic bearing 1 iscomposed of flexible plates 2 of rubber or the like having theviscoelastic property and rigid plates 3 of steel or the like havingrigid property, said plates being laminated alternately.

The following is a detailed description of the material from which theflexible plates are made.

Hysteresis ratio:

In general, the value of loss tangent (tan δ) is used as a measure torepresent the hysteresis loss characteristics and dampingcharacteristics of a material. However, tan δ is not an adequateparameter to describe the hysteresis loss characteristics of a materialfor anti-seismic bearings which undergo as great deformation as 100 to200% at the time of earthquake, because it is a quantity which ismeasured as the delay of response to the stimuli of very small amplitudeapplied to a material.

For this reason, in the present invention, the hysteresis ratio (h₁₀₀)of a material at 100% deformation at 25° C. is used as a measure of theloss characteristics. Incidentally, the h₁₀₀ is given by the ratio ofarea OABCO to area OABHO in the stress-strain curve in FIG. 2 which isobtained at an extension rate of 200 mm/min.

As mentioned above, the h₁₀₀ should preferably be as great as possiblefrom the standpoint of damping effect. However, a material having a highh₁₀₀ has a large amount of plastic deformation. For a given material tobe satisfactory in both characteristics, the value of h₁₀₀ at 25° C.should be in the range of 0.15≦h₁₀₀ ≦0.60, preferably 0.20≦h₁₀₀ ≦0.55.Loss tangent tan δ:

The anti-seismic bearings support the weight of a building at all times;therefore, they are subject to creeping and the creeping of theanti-seismic bearings leads to the sinking of a building. What isimportant to note here is that the initial deformation of the materialby the dead weight of a building is as small as 1% or less. Thus theeffect of the loss characteristics of a material on the creepcharacteristics of an anti-seismic bearing occurs in such a small amountof strain.

Creep should be as small as possible from the standpoint of buildingstability. Therefore, the tan δ to represent the loss characteristicsshould preferably be small in this strain region. In other words, thetan δ measured by dynamic test at a strain of 0.01%, 5 Hz, at 25° C.should be in the range of 0.010≦tan δ≦0.194, preferably 0.020≦tanδ≦0.190, and more preferably 0.025≦tan δ≦0.185. Temperature dependenceof modulus:

The most important factors which affect the seismic isolationcharacteristics are the longitudinal spring constant and lateral springconstant. They are directly proportional to the modulus of a material.

Anti-seismic bearings are exposed to the atmosphere at all times whenthey are in use. The atmospheric temperature would be lower than -10° C.in winter and higher than 30° C. in summer. The modulus of a rubbermaterial is dependent more or less on temperature, and a rubber materialbecomes rigid at low low temperatures. In addition, the greater the lossof a material, the greater the temperature dependence.

According to the present invention, the material should have a moduluswhich is as little temperature-dependent as possible, and the ratio ofthe storage modulus measured by dynamic test at a strain of 0.01%, 5 Hz,at -10° C. to the storage modulus at a strain of 0.01%, 5 Hz, at 30° C.should be in the range of ##EQU1##

The material for the flexible plates which satisfies the abovementionedconditions includes a variety of rubbers such as ethylene propylenerubber (EPR, EPDM), nitrile rubber (NBR), butyl rubber, halogenatedbutyl rubber, chloroprene rubber (CR), natural rubber (NR), isoprenerubber (IR), styrene butadiene rubber (SBR), and butadiene rubber (BR).Preferable among them are halogenated butyl rubber, EPR, EPDM, CR, NR,IR, BR, and SBR. They may be advantageously used in combination with oneanother.

A preferred high-loss rubber compound is obtained by blending 100 partsby weight of natural rubber-based compound with 15 to 100 parts byweight of cyclopentadiene resin and/or dicyclopentadiene resin. Thiscompound has the high-loss characteristics of natural rubber and thegreatly improved temperature dependence, fracture characteristics, andadhesion characteristics.

It was found that a specific cyclopentadiene resin or dicyclopentadieneresin improves the processability of rubber and the characteristicproperties of rubber because of its chemical and physical reactions withrubber which take place at the curing time. The cyclopentadiene resin ordicyclopentadiene resin can be more readily compounded with rubber thanordinary process oil. They affect heat generation and rupturecharacteristics only a little. The natural rubber-based compoundincorporated with these resins are less temperature-dependent andsuperior in rubber-metal adhesion. In addition, unlike process oil, theyhardly migrate after use for a long period of time and they keep therubber compound stable over a long period of time.

The cyclopentadiene resin or dicyclopentadiene resin to be incorporatedinto a natural rubber-based compound is a petroleum resin composedmainly of cyclopentadiene or dicyclopentadiene. It includes copolymersof cyclopentadiene or dicyclopentadiene with a polymerizable olefinhydrocarbon and also includes polymers of cyclopentadiene and/ordicyclopentadiene. These resins should contain more than 30%, preferablymore than 50% of cyclopentadiene or dicyclopentadiene or a mixturethereof.

The olefin hydrocarbon copolymerizable with cyclopentadiene ordicyclopentadiene includes olefin hydrocarbons such as 1-butene,2-butene, isobutylene, 1-pentene, 2-pentene, 2-methyl-1-butene,3-methyl-1-butene, and 2-methyl-2-butene; diolefin hydrocarbons such asbutadiene, isoprene, and 3-methyl-1,2-butadiene; and vinyl-substitutedaromatic hydrocarbons such as styrene, α-methylstyrene, andvinyl-toluene. They can be copolymerized with cyclopentadiene ordicyclopentadiene through Friedel-Crafts reaction in the presence of aproper catalyst.

In view of the molecular weight and the reactivity of the double bond,the cyclopentadiene resin or dicyclopentadiene resin should preferablyhave a softening point of 50° to 200° C. (measured by ring and ballmethod according to JIS K-5902) and a bromine number of 40 to 150(measured according to ASTM D-1158-57T) so that they produce a desiredeffect on the vulcanized rubber. The amount of the cyclopentadieneand/or dicyclopentadiene to be incorporated into natural rubber-basedcompound is 15 to 100 parts by weight, preferably 20 to 80 parts byweight for 100 parts by weight of natural rubber-based compound, so thatthe resulting rubber compound has the desired processability and losscharacteristics.

The natural rubber-based compound may contain BR, NBR, butyl rubber,halogenated butyl rubber, and/or chloroprene rubber. It may also containa filler, antioxidant, plasticizer, softener, oil, and other commonlyused additives, according to need. The resulting rubber compound may beincorporated with a filler, plasticizer, softener, oil antioxidant, andother commonly used additives.

The material constituting the rigid plate 3 is a metal, ceramics,plastics, FRP, polyurethane, wood, paperboard, slate, or decorativelaminate. The shape of the flexible plate and rigid plate may be circle,square, pentagon, hexagon, or polygon. The bonding of the flexible plateto the rigid plate may be accomplished by the aid of an adhesive orcovulcanization.

Since the anti-seismic bearings are exposed to the atmosphere at alltimes while they are in use, they are degraded by air, moisture, ozone,ultraviolet light, radiation (in the case of nuclear power station), andsea wind (in the case of seacoast buildings) over a long period of time.In addition, the anti-seismic bearings supporting a building receive acompressive load at all times, and the compressive load produces aconsiderable amount of local strain in the surface of the rubber layerof 100 to 200% in the case of great earthquake. Such stress and strainpromote degradation. Therefore, it is desirable for the peripheral edgesof the rigid plates 3 and flexible plates 2 of the anti-seismic bearing1 to be covered with a covering layer 4 of a rubber material havingsuperior weather resistance.

The rubber material for the covering layer should preferably be arubbery polymer having superior weather resistance. Examples of suchpolymers include butyl rubber, acryl rubber, polyurethane, siliconerubber, fluororubber, polysulfide rubber, ethylene propylene rubber (EPRand EPDM), Hypalon, chlorinated polyethylene, ethylene-vinyl acetaterubber, epichlorohydrin rubber, and chloroprene rubber. Preferable amongthem from the standpoint of weather resistance are butyl rubber,polyurethane, ethylene propylene rubber, Hypalon, chlorinatedpolyethylene, ethylene-vinyl acetate rubber, and chloroprene rubber.Preferable among them from the standpoint of adhesion to the rubberconstituting the flexible plates are butyl rubber, ethylene propylenerubber, and chloroprene, with ethylene propylene rubber being mostdesirable.

These rubber materials may be used individually or in combination withone another. For the improvement of their physical properties, they maybe blended with commercial rubber such as natural rubber, isoprenerubber, styrene butadiene rubber, butadiene rubber, and nitrile rubber.In addition, these rubber materials may be incorporated with additivessuch as filler, antioxidant, plasticizer, softener, and oil which arecommonly used for rubber processing.

Among the above-mentioned covering rubber materials, ethylene propylenerubber is superior in ozone resistance, radiation resistance, oxidationresistance, UV light resistance, heat aging resistance, and lowtemperature resistance. Ethylene propylene rubber is improved inprocessability when it is incorporated with cyclopentadiene resin ordicyclopentadiene resin. In addition, these resins improve theproperties of the rubber through the chemical reaction and physicalaction that take place at the curing time.

When 100 parts by weight of a rubber compound composed mainly ofethylene propylene rubber is incorporated with 10 to 40 parts by weight,preferably 10 to 35 parts by weight, of cyclopentadiene resin and/ordicyclopentadiene resin and 5 to 20 parts by weight of rosin derivative,the resulting rubber compound is greatly improved in adhesion to rubberand metal, processability, and rupture property, while keeping thesuperior weather resistance of ethylene propylene rubber.

The cyclopentadiene resin or dicyclopentadiene resin to be incorporatedinto a rubber compound composed mainly of ethylene-propylene rubber maybe the same one as mentioned above which is incorporated into naturalrubber to prepare a high-loss rubber compound suitable as a material forthe flexible plates.

The rosin derivative is composed mainly of a mixture of carboxylic acidssuch as abietic acid and pimaric acid, and it includes, for example,rosin ester, polymeric rosin, hydrogenated rosin, hardened rosin, highrosin, disproportionated rosin zinc, and modified rosin.

The ethylene-propylene rubber includes ethylene-propylene diene rubber(EPDM) containing diene as a third component, ethylene-propylene rubber(EPR) not containing a third component, oil-extended ethylene-propylenediene rubber, and oil-extended EPR. The ethylene-propylene rubber may beblended with general-purpose rubber such as NR, BR, and SBR for theimprovement of processability, according to need.

The high weather resistant rubber compound may be incorporated with avulcanization accelerator selected according to the application.Examples of the vulcanization accelerator include thiazole typeaccelerators, guanidine type accelerators, thiuram type accelerators,and thiocarbamate type accelerators. Preferable among them areN-cyclohexyl-2-benzothiazole sulfenamide, dibenzothiazyl disulfide,tetramethylthiuram monosulfide, 2-mercaptobenzothiazole,2-mercaptobenzothiazole cyclohexylamine salt, tetra-2-ethylhexylthiuramdisulfide, zinc di-2-ethylhexyldicarbamate, and diphenylguanidine.Particularly desirable among them are N-cyclohexyl-2-benzothiazolesulfenamide and diphenyl guanidine. The desired amount of thevulcanization accelerator is 0.5 to 5 parts by weight. The high weatherresistant rubber compound may contain a filler, antioxidant,plasticizer, softener, and oil which are commonly used for rubberprocessing.

The covering layer 4 should preferably be as thick as possible toproduce the maximum effect of protecting the rubber inside. On the otherhand, a thick covering layer increases the production cost and requiresa prolonged vulcanization time. With these factors taken into account,the thickness of the covering layer 4 should be 1 to 30 mm, preferably 2to 20 mm, and more preferably 3 to 15 mm. In the case where theanti-seismic bearings are required to have fireproofness, the thicknessof the covering layer may exceed 30 mm.

The covering layer 4 may be firmly bonded to the rigid plates 3 andflexible plates 2 by any of the following methods.

(a) The rubber material for the flexible plates 2 (referred to asinternal rubber) and the rubber material for the covering layer 4(referred to as covering rubber) are vulcanized simultaneously.

(b) The internal rubber is vulcanized first and subsequently thecovering rubber is vulcanized.

(c) The internal rubber and the covering rubber are vulcanizedseparately and then they are bonded together with an adhesive.

The bonding of the internal rubber and covering rubber may be promotedby interposing a third rubber layer between them which adheres well toboth of them. In addition, the internal rubber and/or covering rubbermay be incorporated with additives for the improvement of adhesion.

The anti-seismic bearings undergo great shear deformation as thebuilding on them rocks when an earthquake occurs. This shear deformationleads to an extremely great local strain at the surface layer of theflexible plate adjacent to the flange of the anti-seismic bearing, andthis local strain leads to damage and rupture of the anti-seismicbearing.

This local strain results from the flexural deformation of the rigidplate adjacent to the flange. To prevent this local strain, either ofthe following structures should be adopted. (I) The rigid plate adjacentto the flange has a higher flexural rigidity than the rigid plate at thecenter. (II) The flexible plate adjacent to the flange has a highertensile strength than the flexible plate at the center.

In the case of structure (I), the rigid plates of varied flexuralrigidity should be arranged so as to satisfy the following conditions.Assuming that the rigid plates are designated S₁, S₂, S₃, . . . S_(M)(S₁ being adjacent to the flange and S_(M) being at the center) andtheir respective rigidity values at 25° C. are E_(S).sbsb.1,E_(S).sbsb.2, E_(S).sbsb.3, . . . E_(SM), the following relation shouldbe established between the flexural rigidity E_(S).sbsb.1 of the rigidplate S₁ and the flexural rigidity E_(SM) of the rigid plate S_(M).##EQU2## In addition, the following relation should be establishedbetween the flexural rigidity E_(S).sbsb.2 of the rigid plate S₂ and theflexural rigidity E_(SM) of the rigid plate S_(M). ##EQU3## Ifnecessary, the flexural rigidity E_(S).sbsb.3 of the rigid plate S₃ maybe greater than the flexural rigidity E_(SM) of the rigid plate S_(M).

In this case, the respective rigidity values E_(S).sbsb.1, E_(S).sbsb.2,E_(S).sbsb.3, . . . E_(SM) of the rigid plates S₁, S₂, S₃, . . . S_(M)may be set up so as to satisfy the following conditions. E_(S).sbsb.1≦E_(S).sbsb.2 ≦E_(S).sbsb.3 ≦ . . . ≦E_(SM) (provided that the case inwhich E_(S).sbsb.1 =E_(S).sbsb.2 =E_(S).sbsb.3 = . . . =E_(SM) isexcluded). It is also possible to set up randomly such that each ofE_(S).sbsb.1, E_(S).sbsb.3, and E_(S).sbsb.7 (the flexural rigidity ofthe 7th rigid plate S₇ counted from the flange side) is greater thanE_(SM). In short, according to the present invention, the rigid plateadjacent to the flange should have a higher flexural rigidity than therigid plate at the center. The flexural rigidity of the individual rigidplates should be properly established according to the estimateddirection and magnitude of shocks applied to the anti-seismic bearings.

There are several possible ways to make the flexural rigidity of therigid plate adjacent to the flange higher than that of the rigid plateat the center. The following two ways are adequate. (1) The rigid plateadjacent to the flange and the rigid plate at the center are made of thesame material but the former is thicker than the latter. (2) The rigidplate adjacent to the flange and the rigid plate at the center are madeof different materials, the material for the former having a higherflexural rigidity than that for the latter.

In the case of (1), the plate thickness to give a flexural rigidityrequired is easily calculated because doubling the plate thicknessincreases the flexural rigidity 2³ times.

In the case of structure (II), the flexible plates of varied tensilestrength should be arranged so as to satisfy the following conditions.Assuming that the flexible plates are designated R₁, R₂, R₃, . . . R_(M)(R₁ being adjacent to the flange and R_(M) being at the center) andtheir respective values of tensile strength at 100% elongation (modulus100) at 25° C. are E_(R).sbsb.1, E_(R).sbsb.2, E_(R).sbsb.3, . . .E_(RM), the following relation should be established between the tensilestrength E_(R).sbsb.1 of the flexible plate R₁ and the tensile strengthE_(RM) of the flexible plate R_(M). ##EQU4## In addition, the followingrelation should be established between the stress E_(R).sbsb.2 of theflexible plate R₂ and the stress E_(RM) of the flexible plate R_(M).##EQU5## If necessary, the tensile strength E_(R).sbsb.3 of the flexibleplate R₃ may be greater than the tensile strength E_(RM) of the flexibleplate R_(M).

In this case, the respective values of tensile strength E_(R).sbsb.1,E_(R).sbsb.2, E_(R).sbsb.3, . . . E_(RM) of the flexible plates R₁, R₂,R₃, . . . R_(M) may be set up so as to satisfy the following conditions.E_(R).sbsb.1 ≦E_(R).sbsb.2 ≦E_(R).sbsb.3 ≦ . . . ≦E_(RM) (provided thatthe case in which E_(R).sbsb.1 =E_(R).sbsb.2 =E_(R).sbsb.3 = . . .=E_(RM) is excluded). It is also possible to set up such that each ofE_(R).sbsb.1, E_(R).sbsb.3, and E_(R).sbsb.7 (the tensile strength ofthe 7th rigid plate R₇ counted from the flange side) is greater thanE_(RM).

There are several possible ways to make the tensile strength of theflexible plate adjacent to the flange higher than that of the flexibleplate at the center. The following two ways are adequate. (1) Theflexible plate adjacent to the flange and the flexible plate at thecenter are made of the same base material but the base material for theformer contains more filler than that for the latter. (2) The flexibleplate adjacent to the flange and the flexible plate at the center aremade of different base materials, the base material for the formerhaving a higher tensile strength than that for the latter.

According to the present invention, it is desirable that the flexibleplate R_(M) at the center should have a tensile strength E_(RM) of 5 to40 kg/cm² at 100% elongation at 25° C. The above-mentioned arrangementreduces the local strain resulting from the flexural deformation of therigid plate adjacent to the flange. This minimizes the possibility ofthe anti-seismic bearing being damaged and broken by local strain.

The anti-seismic bearing formed by laminating flexible plates and rigidplates has a disadvantage that an excessive stress concentrates at thatpart of the flexible plate which is in contact with the edge of therigid plate and the concentrated stress damages that part.

This disadvantage can be overcome in this invention by adopting thefollowing structure. The edge of the rigid plate is finished round andcovered with a flexible material, so that all the rigid plates areembedded in the flexible material.

FIG. 4 is a longitudinal sectional view of the anti-seismic bearingconstructed as mentioned just above. The anti-seismic bearing 1 isformed by laminating the flexible plates 2 of viscoelastic rubber or thelike and the rigid plates 3 of steel plate or the like. In this example,the periphery of the rigid plate 3 has a round curve as shown in FIG. 5(a partly enlarged view of the part indicated by V in FIG. 4). Theperiphery 3a is covered with the same material as the flexible plate 2(preferably the above-mentioned rubber material 15 having superiorweather resistance), so that it is isolated from the atmosphere. In thisinvention, the rigid plate 3 is completely covered with the rubbermaterial 15 and therefore the rigid plate 3 is protected from corrosionby the atmosphere. Covering the periphery 3a of the rigid plate 3 withthe rubber material 15 and finishing the periphery 3a of the rigid plate3 round minimize the local stress applied to the flexible material incontact with the periphery 3a.

In this example, the periphery 3a of the rigid plate 3 should have aradius of curvature (R) which satisfies the following condition.##EQU6## and preferably ##EQU7## (where h represents the thickness ofthe rigid plate 3).

In the case where ##EQU8## the peripheral curve should be connected tothe straight part with a smooth transition curve as shown in FIG. 6. Theexample shown in FIG. 6 produces the same effect as the examples shownin FIGS. 4 and 5.

The local stress that occurs in the rubber material in contact with theperiphery of the rigid plate 3 is gradually reduced as the thickness ofthe flexible plate 2 is increased. However, the reduction of localstress levels off beyond a certain thickness. In this invention,therefore, the thickness (t mm) of the rubber material (15) should be inthe range of 1≦t≦20, preferably 2≦t≦15, and more preferably 3≦t≦10.

The effect of the example of the invention is demonstrated as follows:In the case where the rigid plate 3 is a 3 mm thick round iron plate 220mm in diameter and the flexible plate 2 is a 22 mm thick round rubberplate 220 mm in diameter, the maximum local stress reaches 55% when aload is applied to compress the rubber plate 2 by 4% on an average. Incontrast, in the case of the example shown in FIGS. 4 and 5 (in which##EQU9## and t=5 mm), the maximum stress was reduced to 14%.

The anti-seismic bearing not only isolates a building from seismicshocks but also exhibits the vibration isolating and dampingperformance.

The anti-seismic bearing assembly is composed of high-dampinganti-seismic bearings and conventional low-damping anti-seismicbearings, the former exhibiting the damping performance required forearthquake protection and the latter supporting a part or all of thevertical load of a building or equipment. Because of this combination,the creeping of the assembly is limited to a very low level.

FIG. 7 shows a longitudinal section view showing the anti-seismicbearing assembly 30 installed between the building 40 and the foundation50 in an example of the invention.

The anti-seismic bearing assembly 30 is composed of the high-dampinganti-seismic bearing 10 and the low-damping anti-seismic bearing 20arranged in parallel. In FIG. 7, flanges are indicated by referencenumerals 6, 7, 8, and 9. Each of the anti-seismic bearings 10 and 20 isformed by laminating alternately flexible plates (11, 13) of rubber orthe like and rigid plates (12, 14) of steel or the like.

The ratio (in terms of number and sectional area) of the high-dampinganti-seismic bearings to the low-damping anti-seismic bearings to beinstalled in parallel, and the ratio of the rigid plates (12, 14) to theflexible plates (11, 13) should be determined according to theearth-quake protection performance required for a particular building orequipment for which the anti-seismic bearing assembly is installed, thespring constant, the temperature dependence of spring constant, thedamping effect, and the creep resistance.

The flexible plate 11 of the high-damping anti-seismic bearing 10 shouldbe made of high-damping rubber or high-hysteresis rubber characterizedby that the hysteresis ratio h₁₀₀ at 100% deformation at 25° C. is 0.25to 0.70, and the ratio E(-10)/E(30) is 1.0 to 3.0, where E(-10) is astorage modulus at 0.01% deformation, 5 Hz, at -10° C. and E(30) is astorage modulus at 0.01% deformation, 5 Hz, at 30° C.

The flexible plate 13 of the low-damping anti-seismic bearing 20 shouldbe made of low-damping rubber or low-hysteresis rubber characterized bythat the hysteresis ratio h₁₀₀ at 100% deformation at 25° C. is 0.05 to0.20, and the ratio E(-10)/E(30) is 1.0 to 1.5, where E(-10) is astorage modulus at 0.01% deformation, 5 Hz, at -10° C. and E(30) is astorage modulus at 0.01% deformation, 5 Hz, at 30° C.

The preferred ranges are given above for reasons mentioned in theprevious sections concerning the hysteresis of ratio of material and thetemperature dependence of modulus of material.

The high-hysteresis rubber material should preferably have an h₁₀₀ (at25° C.) in the range of 0.25≦h₁₀₀ ≦0.70.

The low-hysteresis rubber material should preferably have an h₁₀₀ (at25° C.) in the range of 0.05≦h₁₀₀ ≦0.20.

In the case of high-hysteresis rubber, the temperature dependence ofmodulus should be such that the ratio of the storage modulus measured bydynamic test at a 0.01% strain, 5 Hz, at -10° C. to the storage modulusat a 0.01% strain, 5 Hz, at 30° C. is in the range of ##EQU10##

In the case of low-hysteresis rubber, the ratio should be in the rangeof ##EQU11##

The high-hysteresis rubber material used in the present invention may beselected from any materials that satisfy the above-mentioned conditions.A preferred example is a vulcanized rubber composed of 100 parts byweight of one or more than one kind of rubber selected from thefollowing and 15 to 100 parts by weight of cyclopentadiene resin ordicyclopentadiene resin. Ethylene-propylene rubber (EPR, EPDM), nitrilerubber (NBR), butyl rubber, halogenated butyl rubber, chloroprene rubber(CR), natural rubber (NR), isoprene rubber (IR), styrene butadienerubber (SBR), and butadiene rubber (BR). This vulcanized rubber is alsosuperior in adhesion to metal. The rubber material may be incorporatedwith a filler, plasticizer, softener, and oil which are commonly usedfor rubber processing.

The low-hysteresis rubber material used in the present invention may beselected from any materials that satisfy the above-mentioned conditions.

The material constituting the rigid plates 12 and 14 in the anti-seismicbearing assembly may be a metal (such as steel), ceramics, plastics,FRP, polyurethane, wood, paperboard, slate, and decorative laminate. Theshape of the rubber plates 11 and 13 and the rigid plates 12 and 14 maybe circle, square, pentagon, hexagon, or polygon. The bonding of therubber plate to the rigid plate may be accomplished by the aid of anadhesive or covulcanization.

Since the anti-seismic bearing assembly is exposed to the atmosphere atall times while in use, it is degraded by air, moisture, ozone,ultra-violet light, radiation (in the case of nuclear power station),and sea wind (in the case of seacoast buildings) over a long period oftime. Therefore, it is desirable that the high-damping anti-seismicbearing 10 and the low-damping anti-seismic bearing 20 should be coveredwith the above-mentioned weather resistant rubber material as shown inFIG. 3.

The anti-seismic bearing assembly as shown in FIG. 7 is an example ofthe invention, and it should not be construed to limit the scope of theinvention. In an alternative example, for instance, the high-dampinganti-seismic bearing 10 and the low-damping anti-seismic bearing 20 maybe integrally combined as shown in FIG. 8. In the case of theanti-seismic bearing assembly as shown in FIG. 8, the high-dampinganti-seismic bearing 20 is inserted into the hollow of the low-dampinganti-seismic bearing 10. The arrangement of the two anti-seismicbearings may be reversed.

The flexible plates that meet the above-mentioned three requirementspermit the anti-seismic bearing to produce the outstanding seismicisolation effect as well as the good damping effect. Therefore, theanti-seismic bearing of the invention absorbs seismic shocks andisolates the building from ground motion. Thus it protects the building,piping, wiring, and other equipment from earthquake and stably supportsthe building.

The anti-seismic bearing assembly is composed of the high-dampinganti-seismic bearings and the low-damping anti-seismic bearings. Theformer produces the seismic isolation effect and good damping effect,and the latter produces the good seismic isolation effect and exhibitsthe good creep resistance. Therefore, the anti-seismic bearing assemblyreduces shocks transmitted to the building and firmly support thebuilding over a long period of time. The anti-seismic bearing assemblyproduces the seismic isolation effect as well as the damping effect.

The flexible plates constituting the anti-seismic bearing or theflexible plates constituting the high-damping anti-seismic bearing ofthe anti-seismic bearing assembly are made of a high-loss rubbercompound composed of 100 parts by weight of natural rubber-basedcompound and 15 to 100 parts by weight of cyclopentadiene resin and/ordicyclopentadiene resin. This rubber compound provides the superiorhigh-loss characteristics, rupture characteristics, elongationcharacteristics, temperature dependence, rubber-metal adhesion, andlong-term stability.

The anti-seismic bearing and the anti-seismic bearing assembly areconstructed such that the peripheral parts of the flexible plates andrigid plates are covered with a high weather-resistant rubber compoundcomposed of 100 parts by weight of ethylene-propylene rubber, 10 to 40parts by weight of cyclopentadiene resin and/or dicyclopentadiene resin,and 5 to 20 parts by weight of rosin derivative. This rubber compoundprotects the anti-seismic bearing over a long period of time because ofits good ozone resistance, radiation resistance, oxidation resistance,heat aging resistance, low-temperature property, adhesion to metal andother rubbers, elongation at break, and mechanical properties.Therefore, the anti-seismic bearing has a very good durability.

The effect of the high-loss rubber compound and high weather-resistantrubber compound suitable in this invention will be demostrated withreference to the following experiment examples.

EXPERIMENT EXAMPLE 1

Rubber compounds of the formulations as shown in Table 1 were produced,and their physical properties were examined. The results are also shownin Table 1.

It is noted from Table 1 that the rubber compound No. 4 (ComparativeExample) has a high temperature dependence and a low elongation at breakbecause it contains a large amount of aromatic oil. In contrast, thehigh-loss rubber compounds Nos. 1 to 3 incorporated withdicyclopentadiene resin are superior in loss characteristics,temperature dependence, rubber rupture characteristics, and adhesion. Inother words, they have well-balanced properties.

                                      TABLE 1                                     __________________________________________________________________________                                        Comparative                               Items             Example 1                                                                           Example 2                                                                           Example 3                                                                           Example 4                                 __________________________________________________________________________    Formulation (parts by weight)                                                 Rubber                                                                        NBR               70    70    70    --                                        BR                30    30    30    --                                        SBR*.sup.3        --    --    --    100                                       Carbon black      50    70    90    130                                       Dicyclopentadiene resin*.sup.1                                                                  30    50    70    --                                        Aromatic oil      --    --    --    110                                       High styrene SBR*.sup.2                                                                         --    --    --    10                                        Sulfur            1.5   1.5   1.5   1.5                                       Physical properties                                                           Loss characteristics h.sub.100 *.sup.4                                                          0.38  0.51  0.60  0.52                                      Temp. dependence E(-10)/E(+30)*.sup.5                                                           1.49  1.57  1.67  3.15                                      Elongation at break Eb (%)*.sup.6                                                               860   870   760   700                                       Tensile strength at 100%                                                                        10.6  9.6   10.5  11.0                                      strain Md.sub.100 (kg/cm.sup.2)*.sup.7                                        __________________________________________________________________________     Note to Table 1                                                               *.sup.1 : Polymer of dicyclopentadiene having a softening point of            116° C. and a bromine number of 65.                                    *.sup.2 : Styrene 55% and butadiene 45%                                        *.sup.3 : Styrene 23.5%                                                      *.sup.4 : The ratio of hysteresis at 100% deformation ot 25° C. It     is a measure of loss characteristics. Extension speed at 200 mm/min. The      h.sub.100 is given by the ratio of area OABCO to area OABHO of the            stressstrain curve shown in FIG. 2.                                           *.sup.5 : The ratio of the storage modulus at -10° C. to the           storage modulus at +30° C., both measured by dynamic test at a         0.01% strain, 12 Hz. It is an index representing the temperature              dependence.                                                                   *.sup.6 : Elongation at break measured at an extension speed of 300 mm/mi     at 25° C.                                                              *.sup.7 : Stress at 100% strain measured at an extension speed of 300         mm/min at 25° C.                                                  

EXPERIMENT EXAMPLE 2

Rubber compounds of the formulations as shown in Table 2 were produced,and their physical properties were examined. The results are also shownin Table 2. The physical properties were all measured at 25° C.

It is noted from Table 2 that the rubber compounds Nos. 9 and 10(Comparative Examples) have a low elongation at break and are poor inadhesion to iron plates and natural rubber. In contrast, thehigh-weather resistant compounds Nos. 5 and 8 incorporated withdicyclopentadiene resin and high rosin have a high elongation at breakand breaking strength and are superior in adhesion to metal and naturalrubber compounds.

                                      TABLE 2                                     __________________________________________________________________________                       Example                                                                            Example                                                                            Example                                                                            Example                                                                            Comparative                                                                          Example                         Items              5    6    7    8    9      10                              __________________________________________________________________________    Formulation (parts by weight)                                                 Rubber:                                                                       EPDM               70   70   70   70   70     100                             NR                 30   30   30   30   30     --                              ISAF carbon        40   40   40   40   30     30                              Dicyclopentadiene resin*.sup.1                                                                   18   27   14   21   --     --                              High rosin         9    10   14   9    --     --                              Spindle oil        --   --   --   --   20     20                              Sulfur             1.5  1.5  1.5  1.5  1.5    1.5                             Vulcanization accelerator*.sup.2                                              CZ                 2.7  2.5  2.5  2.5  --     --                              TS                 --   --   --   --   2.3    2.3                             DPG                --   --   --   1    --     --                              Antioxidant 810NA  1    1    1    1    1      1                               Physical properties                                                           Modulus at 100% elongation (kg/cm.sup.2)                                                         17   11   14   14   23     19                              Elonagation at break (%)                                                                         700  840  800  780  370    280                             Breaking strength (kg/cm.sup.2)                                                                  141  110  152  156  78     80                              Rubber/rubber bond strength (kg/in)*.sup.3                                                       70   50   70   80   20     6                               Rubber/metal bond strength (kg/in)*.sup.4                                                        87   80   80   87   40     35                              __________________________________________________________________________     Note to Table 2                                                               *.sup.1 : Polymer of dicyclopentadiene having a softening point of            116° C. and a bromine number of 65.                                    *.sup.2 : CZ: N--cyclohexyl2-benzothiazole sulfenamide TS:                    Tetramethylthiuram monosulfide DPG: Diphenyl guanidine Antioxidant 810NA:     N--isopropylN'--phenylp-phenylenediamine                                      *.sup.3 : Adhesion of the sample to a natural rubber compound (Rubber         compound No. 14 mentioned layer)                                              *.sup.4 : Adhesion of the sample to a metal.                             

EXPERIMENT EXAMPLE 3

The weather resistance of rubber compounds Nos. 5-7 shown in Table 2 wascompared with that of an ordinary natural rubber compound No. 14(composed of 100 parts by weight of natural rubber, 20 parts by weightof HAF carbon black, 10 parts by weight of spindle oil, 1.5 parts byweight of sulfur, and 1 part by weight of antioxidant). The results areshown in Table 3.

                                      TABLE 3                                     __________________________________________________________________________                                      Comparative                                 Items           Example 11                                                                          Example 12                                                                          Example 13                                                                          Example 14                                  __________________________________________________________________________    Rubber compound No. 5 No. 6 No. 7 NR-based                                    Ozone resistance*.sup.1                                                                       No cracking after 2000 hours                                                                    Many cracks                                                                   after 2 hours                               Heat aging resistance*.sup.2                                                  Retention of elongation at break                                                              0.77  0.80  0.75  0.30                                        Retention of breaking strength                                                                0.74  0.82  0.72  0.09                                        Cycles of flexing until rupture                                                               7 × 10.sup.3                                                                  12 × 10.sup.3                                                                 5 × 10.sup.3                                                                  20                                          __________________________________________________________________________     *.sup.1 : 50% stretched sample in 90 pphm at 40° C.                    *.sup.2 : Measured at 25° C. after heataging in an air oven at         100° C. for 20 days.                                              

It is noted from Table 3 that the high weather resistant rubbercompounds suitable for use in the invention are superior in ozoneresistance, and have high retention values of elongation, breakingstrength, and flex resistance after heat aging. Apparently, they areoutstanding in heat aging resistance.

What is claimed is:
 1. An anti-seismic bearing comprising a plurality ofrigid plates and viscoelastic flexible plates laminated alternately,said flexible plates being made of a material such that the hysteresisratio at 100% deformation at 25° C. is 0.2 to 0.6, and the ratioE(-10)/E(30) is 1.0 to 3.0, where E(-10) is a storage modulus at 0.01%deformation, 5 Hz, at -10° C. and E(30) is a storage modulus at 0.01%deformation, 5 Hz, at 30° C.
 2. An anti-seismic bearing as set forth inclaim 1, wherein the flexible plates are made of a material such thatthe hysteresis ratio at 100% deformation at 25° C. is 0.20 to 0.55, theloss tangent (tan δ) at 0.01% deformation, 5 Hz, at 25° C. is 0.020 to0.190, and the ratio E(-10)/E(30) is 1.0 to 2.5, where E(-10) is astorage modulus at 0.01% deformation, 5 Hz, at -10° C. and E(30) is astorage modulus at 0.01% deformation, 5 Hz, at 30° C.
 3. An anti-seismicbearing as set forth in claim 1, wherein said flexible plates are madeof a material such that the hysteresis ratio at 100% deformation at 25°C. is 0.20 to 0.60.
 4. An anti-seismic bearing as set forth in claim 1,wherein said flexible plates are made of a material such that the losstangent (tan δ) at 0.01% deformation, 5 Hz, at 25° C. is 0.010 to 0.194.5. An anti-seismic bearing as set forth in claim 1, wherein the rigidplates and flexible plates have peripheral parts covered with a rubbermaterial having good weather resistance.
 6. An anti-seismic bearing asset forth in claim 5, wherein the weather resistant rubber compound iscomposed of 100 parts by weight of rubber whose principal component isethylene-propylene rubber, 10 to 40 parts by weight of cyclopentadieneresin and/or dicyclopentadiene resin, and 5 to 20 parts by weight ofrosin derivative.
 7. An anti-seismic bearing as set forth in claim 5,wherein the weather resistant rubber compound is composed of 100 partsby weight of rubber whose principal component is ethylene-propylenerubber, 10 to 35 parts by weight of cyclopentadiene resin and/ordicyclopentadiene resin, and 5 to 20 parts by weight of rosinderivative.
 8. An anti-seismic bearings as set forth in claim 1, whereinthe rigid plates have round peripheral edges which are covered with aviscoelastic flexible material.
 9. An anti-seismic bearing as set forthin claim 5, wherein the rigid plates have round peripheral edges.
 10. Ananti-seismic bearing as set forth in claim 1, wherein the bearing has atleast one of the following items I and II;(I) the rigid plates situatedat upper and lower portions of the bearing have flexural rigidity higherthan the rigid plate situated in a center of the bearing; (II) theflexible plates situated close to upper and lower portions of thebearing have tensile strength higher than the flexible plate situated ina center of the bearing.
 11. An anti-seismic bearing comprising aplurality of rigid plates and viscoelastic flexible plates laminatedalternately, said flexible plates being made of a material such that thehysteresis ration at 100% deformation at 25° C. is 0.2 to 0.6, and theratio E(-10)/E(30) is 1.0 to 3.0, where E(-10) is a storage modulus at0.01% deformation, 5 Hz, at -10° C. and E(30) is a storage modulus at0.01% deformation, 5 Hz, at 30° C., wherein the flexible plates are madeof a high-loss rubber compound composed of 100 parts by weight of rubberwhose principal component is natural rubber and 15 to 100 parts byweight of cyclopentadiene resin and/or dicyclo-pentadiene resin.
 12. Ananti-seismic bearing as set forth in claim 11, wherein the flexibleplates are made of a high-loss rubber compound composed of 100 parts byweight of rubber whose principal component is natural rubber and 20 to80 parts by weight of cyclopentadiene resin and/or dicyclo-pentadieneresin.
 13. An anti-seismic bearing as set forth in claim 11, wherein therigid plates and flexible plates have peripheral parts covered with arubber material having good weather resistance.
 14. An anti-seismicbearing as set forth in claim 13, wherein the weather resistant rubbercompound is composed of 100 parts by weight of rubber whose principalcomponent is ethylene-propylene rubber, 10 to 40 parts by weight ofcyclopentadiene resin and/or dicyclopentadiene resin, and 5 to 20 partsby weight of rosin derivative.
 15. An anti-seismic bering as set forthin claim 13, wherein the weather resistant rubber compound is composedof 100 parts by weight of rubber whose principal component isethylene-propylene rubber, 10 to 35 parts by weight of cyclopentadieneresin and/or dicyclopentadiene resin, and 5 to 20 parts by weight ofrosin derivative.
 16. An anti-seismic bearing as set forth in claim 13,wherein the rigid plates have round peripheral edges.
 17. Ananti-seismic bearing as set forth in claim 11, wherein the rigid plateshave round peripheral edges covered with a viscoelastic flexiblematerial.
 18. An anti-seismic bearing as set forth in claim 11, whereinthe bearing has at least one of the following items I and II:(I) rigidplates situated at upper and lower portions of the bearing havingflexural rigidity higher than a rigid plate situated in a center of thebearing; (II) flexible plates situated close to upper and lower portionsof the bearing having tensile strength higher than a flexible platesituated in a center of the bearing.
 19. An anti-seismic bearing as setforth in claim 11, wherein said flexible plates are made of a materialsuch that the hysteresis ratio at 100% deformation at 25° C. is 0.20 to0.60.
 20. An anti-seismic bearing as set forth in claim 11, wherein saidflexible plates are made of a material such taht the loss tangent (tanδ) at 0.01% deformation, 5 Hz, at 25° C. is 0.010 to 0.194.